CVE-2016-9773 in ImageMagick
Summary
by MITRE
Heap-based buffer overflow in the IsPixelGray function in MagickCore/pixel-accessor.h in ImageMagick 7.0.3.8 allows remote attackers to cause a denial of service (out-of-bounds heap read) via a crafted image file. NOTE: this vulnerability exists because of an incomplete fix for CVE-2016-9556.
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Analysis
by VulDB Data Team • 08/15/2020
The vulnerability described in CVE-2016-9773 represents a heap-based buffer overflow affecting ImageMagick's pixel accessor functionality, specifically within the IsPixelGray function located in MagickCore/pixel-accessor.h. This issue manifests as an out-of-bounds heap read condition that can be exploited remotely through carefully crafted image files, potentially leading to denial of service attacks against systems processing such media content. The vulnerability is particularly concerning because it stems from an incomplete remediation of a previously identified flaw, CVE-2016-9556, indicating a pattern of insufficiently addressed security gaps in the software's memory management systems.
The technical implementation of this vulnerability resides in the heap memory allocation and access patterns within ImageMagick's image processing pipeline. When the IsPixelGray function processes pixel data from malformed image files, it fails to properly validate buffer boundaries before reading pixel values from heap-allocated memory regions. This oversight allows attackers to construct specially formatted image files that trigger memory access violations when the application attempts to read beyond allocated buffer limits. The heap-based nature of the vulnerability means that the overflow occurs within dynamically allocated memory segments, making it particularly challenging to predict and prevent through standard stack-based buffer overflow protections.
From an operational impact perspective, this vulnerability creates significant risk for organizations relying on ImageMagick for image processing tasks, particularly those handling untrusted user uploads or processing images from external sources. The denial of service condition can result in application crashes, resource exhaustion, or system instability when legitimate users attempt to process maliciously crafted images. This vulnerability is especially dangerous in web applications, content management systems, or any platform where users can upload image files, as it provides a straightforward path for attackers to disrupt service availability without requiring elevated privileges or complex exploitation techniques.
The remediation approach for CVE-2016-9773 requires implementing proper input validation and boundary checking within the IsPixelGray function, ensuring that all pixel access operations verify memory boundaries before reading from heap-allocated structures. Security practitioners should prioritize updating to patched versions of ImageMagick that contain complete fixes for both CVE-2016-9556 and CVE-2016-9773, while also implementing defensive programming practices such as bounds checking, memory sanitization, and input validation at multiple layers of the application stack. Organizations should consider deploying additional security controls including image file validation, sandboxed processing environments, and network-based intrusion detection systems to mitigate potential exploitation attempts. This vulnerability aligns with CWE-121 heap-based buffer overflow patterns and represents a typical ATT&CK technique involving remote code execution through memory corruption vulnerabilities in multimedia processing libraries.
The presence of this vulnerability demonstrates the importance of thorough regression testing when implementing security patches, as the incomplete fix for CVE-2016-9556 created a new attack surface that attackers could exploit. This situation underscores the need for comprehensive vulnerability management processes that not only address individual security flaws but also verify that remediations do not introduce new weaknesses. Security teams should maintain awareness of related vulnerabilities in the same codebase and ensure that all updates are thoroughly tested in staging environments before deployment to production systems.